1. Field of the Invention
The present invention relates generally to a spark ignition timing control system for feedback controlling spark ignition timing of an internal combustion engine. More specifically, the present invention relates to a spark ignition timing control system for a split type multi-cylinder internal combustion engine for advancing spark ignition timing of one combustion chamber relative to the remained combustion chambers in order to improve the engine characteristics with regard to knocking.
2. Background of the Invention
Generally, knocking of an internal combustion engine engine will cause the shortening of its life time. A substantive knocking condition is permitted to continue, the engine will be damaged or injured and its durability will be generally degraded. On the other hand, from the view point of fuel economy and maximizing engine output characteristics, it is desirable to maintain the engine at a trace knocking condition. As is well-known to those skilled in the art, adjustments can be made to the spark advance angle of a spark ignition system for causing knocking on the internal combustion engine. In general, advancement of the spark advance angle, results in a corresponding increase in knocking condition in the engine. Therefore, control of knocking condition can be accomplished by controlling the spark advance angle to correspond to engine knocking conditions and other parameters. In the prior art, there have been developed and proposed various system for keeping the internal combustion engine in a lightly or trace knocking condition by feedback controlling the spark advance angle in order to improve fuel economy and maximize engine output characteristics.
It is also well known that under the knocking condition, engine vibration rapidly increase depending on variations on the internal pressure in the combustion chamber. The engine vibration frequency corresponding to knocking conditions is generally within a range of 6 to 9 KHz. Utilizing this characteristics of the engine, there have been proposed various systems for detecting knocking conditions of an engine by determining the engine vibration. For detecting the engine vibration, there may be provided a vibration sensor on the internal combustion engine which detects the above-mentioned specific range of engine vibration. The detected vibration frequency signal is converted into an analog value which is smoothed and thereafter passed to a comparator where it is compared with the vibration element of the specific frequency range to generate a signal. The signal is integrated per every given crank rotational angle. When the integration value exceeds a predetermined value, the engine is regarded as it being driven in a knock condition and a knocking signal is generated. Corresponding to this knocking signal, the spark advance angle is feedback controlled.
In the split type multi-cylinder internal combustion engine having a plurality of engine combustion chambers, it is preferable to advance the spark ignition timing of one of the combustion chambers, which is hereinafter referred as the "specific chamber", relative to the remaining channels. By so doing, the specific chamber is apt to cause knocking in advance to remained chambers entering into a knocking condition. Adjacent to the specific chamber there is positioned a vibration sensor for determining magnitude of engine vibration and thereby for detecting a knocking condition of the engine. This operation is based on the principle that a specific frequency or magnitude of vibration is generated in a combustion chamber while the chamber is being driven in a knocking condition.
Alternatively, in the above-mentioned system for sensing knocking condition of the engine, even when the engine is unstable driven, for example, under low-load condition where the intake vacuum of an intake manifold is relatively high, the spark ignition advance angle is varied in the specific chamber as well as the remaining chambers. This may cause increasing unstability of the engine and thereby degrade the drivability thereof. Further this will also affect the fuel economy.